document updated 10 years ago, on Dec 10, 2013
On a bicycle, a internal gearbox is a gearbox that's located inside the bicycle frame, above the down-tube. This is very similar to how a motorcycle transmission is mounted.
Many framebuilders have experimented with this design over time, but haven't rolled out bikes to production, because they tend to fairly heavy.
Zerode G-1
The Zerode G-1 is a bicycle that incorporates a internal-gear-hub that's been modified to sit inside the frame.
More info:
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Pinion P1.18
The Pinion P1.18 is actually located near the bottom bracket. However, it requires a substantially modified frame — the bottom bracket area of the frame is very different.
Pictures:
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